Wind turbines are used to produce electrical energy using a renewable resource and without combusting a fossil fuel. Generally, a wind turbine converts kinetic energy from the wind into mechanical energy and then subsequently converts the mechanical energy into electrical power. A conventional horizontal-axis wind turbine includes a tower, a nacelle located at the apex of the tower, and a rotor that is supported by the nacelle. A shaft couples the rotor either directly or indirectly with a rotor assembly of a generator, which is housed inside the nacelle.
A typical generator, which is a species of conventional electrical machines, includes a stator assembly that is a stationary construct and a rotor assembly that moves relative to the stationary stator assembly. Under the principles of Faraday's Law and Lenz's Law, the relative motion induces electrical currents in wire coils associated with the stator assembly. The power output of the generator is determined by the torque applied to the generator's axis of rotation, which serves as a limitation on the peak power output.
While conventional generators are adequate for their intended purpose, improved generators and other types of electrical machines, as well as improved wind turbines and methods for operating generators and other types of electrical machines, are needed.